Disclosed herein is a carrier suitable for use with an electrophotographic developer and an electrophotographic developer containing the carrier.
Carrier particles for use in electrophotographic developers comprise a roughly spherical core, which can be made from a variety of materials and is coated with a polymeric resin. This resin is often placed on the core by a solution coating process. It has been found, however, that carriers prepared by powder coating processes can have numerous advantages over those prepared by solution coated carriers, such as lower expense of manufacture and improved environmental friendliness in that no solvents are used in the manufacturing process.
Powder coating of carriers can be carried out as disclosed in, for example, U.S. Pat. Nos. 4,233,387, 4,935,326, 4,937,166, 5,002,846, 5,015,550, and 5,213,936, the disclosures of each of which are totally incorporated herein by reference. The polymeric resin can be prepared by emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 6,042,981, the disclosure of which is totally incorporated herein by reference, prior to preparation of the powder.
Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. Emulsion aggregation toners can be used in forming print and/or xerographic images. Emulsion aggregation techniques can entail the formation of an emulsion latex of the resin particles by heating the resin, using emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943, the disclosure of which is totally incorporated herein by reference. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in, for example, U.S. Pat. Nos. 5,278,020, 5,290,654, 5,302,486, 5,308,734, 5,344,738, 5,346,797, 5,348,832, 5,364,729, 5,366,841, 5,370,963, 5,403,693, 5,405,728, 5,418,108, 5,496,676, 5,501,935, 5,527,658, 5,585,215, 5,650,255, 5,650,256, 5,723,253, 5,744,520, 5,747,215, 5,763,133, 5,766,818, 5,804,349, 5,827,633, 5,840,462, 5,853,944, 5,863,698, 5,869,215, 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488, 5,977,210, 5,994,020, 6,576,389, 6,617,092, 6,627,373, 6,638,677, 6,656,657, 6,656,658, 6,664,017, 6,673,505, 6,730,450, 6,743,559, 6,756,176, 6,780,500, 6,830,860, and 7,029,817, and U.S. Patent Publication No. 2008/0107989, the disclosures of which are totally incorporated herein by reference.
Polyester EA ultra low melt (ULM) toners have been prepared utilizing amorphous and crystalline polyester resins as disclosed in, for example, U.S. Pat. No. 7,547,499 and U.S. Patent Publication 2011/0097664, the disclosures of each of which are totally incorporated herein by reference. Advantages of these toners include small particle size, the ability to control particle size, shape, and morphology, the ability to incorporate a wax into the particles, low fusing temperature, and the like.
While known materials are suitable for their intended purposes, a need remains for improved carrier compositions. In addition, a need remains for improved developer compositions. Further, a need remains for carriers with desirable triboelectric charging characteristics and desirable conductivity characteristics. In order for desired xerographic development to occur developers must have a certain level of Tribo and Conductivity values. For example: For example when Tribo is too high not enough toner will transfer via electrostatics to the charged latent image or the development system controls may over compensate by raising the TC too high resulting in other failures. Also too low of Tribo and too much toner will transfer to the charged latent image or the development system may over compensate by lowering TC too low to raise the tribo resulting in other failures. Another example could be if the conductivity is too high then voltage breakdown may occur marring the image. Also when conductivity is too low the electric field necessary to transfer the toner might not be able to be achieved.